Colorimetric Detection of Perfluorinated Compounds by All-Polymer Photonic Transducers

We report on the highly sensitive optical and colorimetric detection of perfluorinated compounds in the vapor phase achieved by all-polymer dielectric mirrors. High optical quality and uniformly distributed Bragg reflectors were fabricated by alternating thin films of poly(N-vinylcarbazole) and Hyflon AD polymers as high and low refractive index medium, respectively. A new processing procedure has been developed to compatibilize the deposition of poly(N-vinylcarbazole) with the highly solvophobic Hyflon AD polymer layers to achieve mutual processability between the two polymers and fabricate the devices. As a proof of principle, sensing measurements were performed using the Galden HT55 polymer as a prototype of the perfluorinated compound. The Bragg stacks show a strong chromatic response upon exposure to this compound, clearly detectable as both spectral and intensity variations. Conversely, Bragg mirrors fabricated without fluorinated polymers do not show any detectable response, demonstrating that the Hyflon AD polymer acts as the active and selective medium for sensing perfluorinated species. These results demonstrate that organic dielectric mirrors containing perfluorinated polymers can represent an innovative colorimetric monitoring system for fluorinated compounds, suitable to improve both environmental safety and quality of life

High refractive index hyperbranched polyvinylsulfides for planar one-dimensional all-polymer photonic crystals

We report on the growth and characterization of onedimensional (1D) planar all-polymer photonic crystals (PhC) with high dielectric contrast (Dn50.3) prepared by spin coating using hyperbranched polyvinylsulfide polymers (HB-PVS) as high refractive index material and cellulose acetate as low refractive index material. Solution processable HB-PVS show a near ultraviolet absorption inducing an increased refractive index in the visible-near infrared (n51.68, k51000 nm). HBPVS:Cellulose Acetate Distributed Bragg Reflectors show a very clear fingerprint of the photonic band gap possessing the expected polarized dispersion properties as a function of the incidence angle. Moreover, engineered microcavities tuned on the weak fluorescence spectrum of the HB-PVS show directional fluorescence enhancement effects due to spectral redistribution of the emission oscillator strength. The combination of all these properties testifies the high optical quality of the obtained photonic structures thus indicating HB-PVS as an interesting material for the preparation of such PhC. V

Organic and hybrid photonic crystals

Polymer multilayer structures have attracted increasing attention in the recent years because of the straightforward and low-cost techniques that can be used for their fabrication. When the multilayers are composed of a periodical alternation of two materials with different refractive indexes and with layer thicknesses comparable with the wavelength of light, they take the name of distributed Bragg reflectors (DBR). They behave like planar one-dimensional photonic crystals (PhC) and exhibit a photonic band gap (PBG), a spectral region in which photons with suitable energy and wave vector are not allowed to propagate through the crystal. Moreover, within the PBG and at its edges, modifications of radiative photophysical processes occur. The spectral position, efficiency and linewidth of the PBG can be engineered by modifying the layer thicknesses and the refractive indexes of the two materials. While DBRs grown using inorganic materials are well known, polymer and colloidal particle DBRs are receiving a renewed interest due to the possibility to chemically engineer their structural properties and photonic functions; moreover, they can be free-standing and flexible thus being adaptable to any surface. Furthermore, polymers and porous structures can easily embed many other active materials, paving the way to a myriad of applications. In this chapter, we introduce polymer multilayers and planar microcavities fabricated using the spin coating technique, discussing the different materials employed and manufacturing challenges. We will also review different applications that exploit these kinds of photonic structures ranging from lasing to sensing

Distributed Bragg Reflectors: Morphology of Cellulose Acetate and Polystyrene Multilayers

The optical quality and photonic properties of all-polymer distributed Bragg reflectors are related to the morphology of the layers and the optical responses of the materials. We introduce the X-ray reflectivity method to determine the thickness, the interface- and surface-roughness of cellulose acetate and polystyrene layers which are two polymers often used in the domain of spin casted multilayer systems. Atomic force microscopy and spectroscopic ellipsometry were used as complementary techniques for investigating the surface roughness and the film thickness. The shrinkage and the change of interface roughness of the polymers were investigated up to temperatures of 200 degrees C. Up to 170 degrees C the interface roughness stays constant at about 1 nm while it increases up to 2 nm at 200 degrees C. The thickness of the polystyrene layer remains constant up to 170 degrees C, well above its glass transition temperature T-g. For cellulose acetate a monothonic decrease is observed with increasing temperature. It could be shown, that the change in the optical response of a thermally treated distributed Bragg reflector is related to the change of the layer thickness of cellulose acetate. Spectra of (PS CA)(20)PS distributed Bragg reflectors (DBR) are in a good agreement with calculated spectra with parameters optained from of the X-ray reflectivity measurements

Upper Pleistocene sea level changes and human peopling at the northern margin of the Mediterranean Sea: the S-P-Heritage Project

none20openAndrea Zerboni, Irene M. Bollati, Luca Forti, Silvia Gazzo, Abdelkader Moussous, Giovanni Muttoni, Fabio Negrino, Olivier Notter, Manuela Pelfini, Alessandro Perego, Serena Perini, Luca Ragaini, Eleonora Regattieri, Elena Rossoni-Notter, Alessio Rovere, Deirdre Ryan, Marco Serradimigni, Elisabetta Starnini, Matteo Vacchi, Marta PappalardoZerboni, Andrea; Bollati, Irene M.; Forti, Luca; Gazzo, Silvia; Moussous, Abdelkader; Muttoni, Giovanni; Negrino, Fabio; Notter, Olivier; Pelfini, Manuela; Perego, Alessandro; Perini, Serena; Ragaini, Luca; Regattieri, Eleonora; Rossoni-Notter, Elena; Rovere, Alessio; Ryan, Deirdre; Serradimigni, Marco; Starnini, Elisabetta; Vacchi, Matteo; Pappalardo, Mart